Greenhouse - Orchids
( Originally Published 1920 )
OF the numerous orchids, the following are the important commercial genera with their cultural requirements :
CULTURE OF CALANTHE
These are easily grown in pots or in beds, about one-third space being devoted to drainage by means of a layer of clean sphagnum. The pseudobulbs are then planted in a compost which is made up of one-third chopped sod with the fine soil removed, one-third chopped live sphagnum and leaf mold to which charcoal is added as a sweetener. Calanthes require a winter night temperature of about 5o to. 55 degrees and a day temperature of 65 to 70 degrees F. The plants require an abundance of water during the growing period, but less when the leaves start to drop and blossoming begins. At this stage, only enough water is needed to keep the blossoms from wilting. When the blossoming season is over the plants are given a six weeks' rest. The pots with the pseudobulbs are laid on the side in a dry warm place and the soil kept dry.
CULTURE OF CATTLEYA
These plants require perfect drainage conditions. They thrive best in osmunda fiber pots. On a commercial scale, it is not desirable to cover the plants with moss as this usually harbors slugs which are fond of the blossoms. Cattleyas require frequent syringing with the hose. The temperature required is the same as that for Calanthe. After flowering the pseudobulbs need a rest. In this case they require enough water to prevent them from drying. CattleyŠ thrive best when grown near the glass.
CULTURE OF COELOGYNE
The cultural requirements are the same as for CattleyŠ, the pot culture, however, being preferred. The plants are heavy feeders, hence weak manure water may be applied once every week during the growing season. After flowering the plants are re-potted and kept in a cool house until about September.
CULTURE OF CYPRIPEDIA
These plants require no rest period, hence may be grown the year round. They require a winter night temperature of 60 to 65 degrees F. and a day temperature of about 70 degrees F. As spring approaches a higher temperature may be given, and the glass lightly shaded. However, in the winter the plants require the full sunlight.
CULTURE OF DENDROBIUM
These plants seem to thrive best in small pots or baskets. They also require an abundance of water during the growing season, and a night temperature of about 65 degrees F. When flowers appear the plants become destitute of leaves, at which time only enough water is applied to prevent the pseudo-bulbs from drying.
CULTURE OF LAELIA
These plants require a sunny location and an abundance of overhead water during active growth.
CULTURE OF LYCASTE
These plants need to be kept as cool as possible in the summer; otherwise, the culture is the same as for Cattleya.
CULTURE OF ODONTOGLOSSUM
These plants require an abundance of ventilation, and a cool moist temperature during the summer. They are grown in pots or baskets filled with soil made of equal parts peat, live sphagnum moss, and osmunda fiber.
CULTURE OF ONCIDIUM
These plants require a bright, warm house and are suspended from the rafters in small baskets.
CULTURE OF PHALAENOPSIS
These plants require plenty of ventilation, but too much of it should be avoided. Frequent syringing is necessary and the temperature requirements from 70 to 75 degrees F. at night and about 90 to 95 degrees during the daytime.
CULTURE OF VANDA
These plants require shade after February. They prefer a night temperature of 65 degrees F. and seem to thrive best in baskets near the glass.
SPOT DISEASE OF ORCHIDS
Cause, mechanical injury.
Symptoms. This disease is manifested as minute pale spots on the upper side of the leaf. The spots vary considerably in size, arrangement, and numbers, and may occur on any parts of the foliage irrespective of age. The trouble may be easily over-looked, due to the light color and the superficial nature of the spots. With age, however, the spots may go through the entire tissue of the leaf. The cause of the trouble, as explained by Massee,is of non-parasitic origin. It is brought about by the presence of minute drops of water on the surface of the leaves during very low temperatures while the roots are too copiously supplied with water. The water drops produce a chill which causes the content of the underlying cells to plasmolyze. This is followed by the precipitation of tannin and the disintegration of the cells. The method of control would consist in the careful watering of the plants during cool weather.
Florists are aware of the fact that imported orchids often run out and deteriorate after a year or two of culture under glass. Attention has been called to a similar trouble by Truffant and Hebert. They maintain that deterioration is due to an increase in the percentage of mineral matter and a decrease in the percentage of nitrogen in the deteriorated plants. The trouble, it is believed, is due largely to improper nutrition under cultivation.
LEAF SPOT OF ORCHIDS
This disease is often found on hybrid Calanthes. It is manifested as large and small dead patches on all the parts of the plant. The leaves especially become unsightly, and as a result the blossoms are small and stunted. This disease was first described by Bidgood on greenhouse hybrid Calanthes. The cause of the disease and methods of control are as yet unknown.
BACTERIAL LEAF SPOT OF ORCHIDS
Caused by Bacillus cypripedii Hori.
Symptoms. According to Hori, this disease is prevalent in Japan and is greatly feared there. The disease attacks the most valuable orchids and ruins them in a very short time.
The disease is manifested as light amber-colored spots on the leaf blades. The spots quickly enlarge, and in a few days the entire leaf becomes invaded and discolored. A few days later the diseased foliage turns brownish and later a deep chestnut brown; the upper surface becomes wrinkled, with loss of luster. The lower surface of the leaves, just underneath the spots, rapidly take on a faintly pale color, and only gradually assumes the same color as that of the upper part. If infection takes place on the lower portion of the leaf, the upper half soon becomes yellowish and dies off as a result of lack of food (fig. 59, d.). The rot from the leaves works down to the stem, involving the entire plant.
The disease (also known as brown rot, brown spot) attacks orchids with fleshy, succulent leaves, such as PhalŠnopsis amabilis, Ph. schileriana Cypripedium haynaldium, C. philippinense, C. lŠvigaturn, C. godefroyae. The more susceptible varieties seem to be PhalŠnopsis schilleriana and Cypripedium phillipinense. Infection takes place by means of a wound.
The Organism. Bacillus cypripedii is a medium sized slender rod-shaped organism, rounded at both ends, occurring in chains of 2-3, and motile by means of flagella. On agar it forms a smooth, light grayish white colony with a pearly luster, and a dirty cream-colored growth on potato plugs. It produces a film on bouillon, coagulates milk, and rap-idly dissolves gelatin. It is not known whether the causal organism is the same or closely related to the one described by Peglion under the name of Bacterium oncidii Peg. as causing a disease on orchids. Very little is known of the methods of control. Since infection takes place through a wound, care should be taken to prevent careless washing with a rough sponge. Diseased material should be destroyed by fire.
RUST OF ORCHIDS
Caused by Hemileia oncidii Griff and Maubl.
Symptoms. The disease is characterized by minute yellowish spots, the surfaces of which become covered with an orange-colored powder which is made up of the spores of the causal organism. The spots enlarge, the center turns brownish, while the advancing margin remains an orange rust color. The disease was first described by Griffon and Maublanc, who found it on orchids in greenhouses in France. It is not known whether this rust is of any importance in the United States. The only danger consists in its being imported from abroad with imported plants. The causal organism produces only teleutospores. It feeds on its host by means of haustoria sent into the interior of the cells (fig. 59, d, i-9.).
RUST OF ORCHIDS
Caused by Uredo behnickiana Henn.
Symptoms. This rust does not produce any striking symptoms. Hence it may readily be overlooked. Affected leaves are covered with minute, reddish-colored sori. When mature, the epidermal covering of these sori breaks away and liberates a reddish powder which is made up of thousands of the spores of the fungus. This rust is found on living leaves of Oncidium dasystelis and was described by Hennings as a serious disease of orchids imported to Germany from Brazil. It is not known whether this disease is present in this country. Its introduction should therefore be guarded against. Uredo behnickiana differs from U. onicidii Henn, in that the latter causes rounded thickened red-brown spots on Oncidium lavecanum.
Caused by Sclerotinia fuckeliana (De By.) Fekl.
Greenhouse growers are often troubled with a petal blotch of orchids. This disfigures the blossoms, and consequently ruins their market value. The disease appears as small spots over the entire surface area of the petals. Frequently the spots are bordered by a delicate ring of pink. Perhaps another stage of this disease is marked by the large spots which cause the petals to become disorganized. Affected petals either drop off or stick to the now worthless blossom. On examination of the spotted petals, there will be noticed a gray mold growing on the surface of the affected tissue. This is but the fruiting stalks of the causal organism. This gray mold will also be found on faded blossoms, and if allowed to remain in the greenhouse will saturate the place with the spores of the fungus.
Control. All affected blossoms should be cut off and destroyed. This simple precaution will remove the host upon which the fungus is able to thrive as a saprophyte.
Caused by Nectria bulbicola Henn.
This trouble is manifested as a rot on the pseudo bulbs of Macillaria rufescentis. It was originally found by Hennings on orchids brought in from Venezuela or Trinidad.
There are other Nectria recorded on orchids : Nectria vane Wahrl on root of Vanda suavis, Nectria goroshankianna Wahrl., Nectria (Dialonectria) binotiana Sacc., and Nectria (D.) phyllogena Sacc. on leaves of epiphyte orchids in Brazil.
ANTHRACNOSE OF ORCHIDS
Caused by Physalospora cattleyŠ Maub. and Las.
Symptoms. This trouble is manifested as yellowish light spots the tissue of which becomes soft. When the epidermis is torn away from one of the spots a clear liquid will ooze out. At this stage of the malady infected leaves lose their normal color, collapse, and drop off. Ordinarily there is no fruit of any fungus formed on the spots, but under moist conditions the acervuli of the causal fungus appear. The disease, although attacking the foliage, does its greatest damage to the stems. Infection can take place only through a wound made in the epidermis.
The Organism. It is only the summer stage of the fungus, Gloeosporium macro pus Sacc., which causes the disease on orchids. The same stage also produces a similar disease on foliage of Haya carnosa, Citrus aurantium and Aloes. Its occurrence on orchids was called attention to by Mangin, who found it to be a serious disease of greenhouse orchids in France. It is doubtful if it is yet to be feared in the United States.
Control. Care and vigilance should be exercised to prevent the introduction of the disease to the United States. All infected material should be destroyed by fire and the plants should be sprayed with a standard fungicide.
Caused by Glomerella cincta (B. and C.) S. and S.
The American anthracnose is very prevalent on hothouse orchids. The variety most susceptible to the disease is Sobralia macramtha. The trouble is first noticed by a discoloration on the stems which soon become brown almost to black while the tender interior tissue becomes soft and decayed. Later the spore pustules appear in great abundance on the dead parts. On the leaves the disease works in a way similar to that found on the stems. The trouble, however, nearly always starts from the tip and works downwards (fig. 59, c.). There is usually a distinct line of demarkation between the healthy and the diseased tissue.
The Organism. The conchal or summer stage of the fungus was described by Halsted.* The conidia are elliptic and guttulate. Sete may often be present, but they are generally obscured by the great masses of spores formed in the acervuli. The ascus or winter stage was discovered by Stoneman. The perithecia are flask-shaped, the asci are clavate. The ascospores vary from elliptic to curved in shape.
Control. Before attempting anything else, the source of infection should be removed. All infected plants should be destroyed by fire. Spraying with Bordeaux mixture 4-4-50 will help to protect the plants from becoming infected.
Caused by Colletotrichum bletiŠ Hals.
The beautiful Bletia orchid is often subject to the attacks of an anthracnose, the cause of which is due to a closely associated organism of the Sobralia anthracnose. On the Bletia, the trouble is manifested as a spotting that disfigures the leaves and reduces their usefulness. The spots are almost black and very soft. As this disease progresses, the soft tissue rots and breaks away the fibrous portions. Usually the trouble begins at the tender tips, and causes affected foliage to have a ragged appearance.
The Organism. In structure the organism resembles other Colletotrichums. The acervuli are light brown in color and possess numerous dark seta.
Control. The trouble may be kept in check by spraying with Bordeaux mixture. It is also essential to destroy by fire all dead and diseased material and to prevent them from finding a place in the manure or compost pile.
Caused by Glaeosporium affine Sacc.
This disease has been reported by Sorauer as very serious on cultivated orchids. The trouble is prevalent in overheated hothouses and on plants which have been excessively fertilized.
Symptoms. On the leaves, anthracnose causes a discoloration and a drying which starts at the tip, or at the periphery or border. Usually the youngest foliage is attacked first. In severe cases, the older leaves and even the bulbs become diseased, wither, and dry up. The disease is carried about with infected bulbs. The same trouble also attacks other orchids such as Cattleya Mendelii and Cypripedium laevegatum.
The Organism. In structure, Glaeosporium affine differs very little from other Gleosporiums. The fungus attacks the epidermis, then works into the mesophyllic layer of cells, where the chloroplasts are destroyed. This explains the disappearance of the green coloring matter in the affected parts. The spore pustules are formed under the epidermis, the latter bursting as the spores accumulate. The spores are formed on what appears to be a pseudostroma. The spores are one-celled, hyaline, cylindrical, and often slightly curved. The spores germinate quickly, usually after forty-eight hours. Glaeosporium affine is troublesome on orchids in Europe, but has not yet proved very serious in the United States.
OTHER ORCHID GLOEOSPORIUMS
Glceosporium oncidii Oud.= G. maxillariŠ All. This organism is confined to Ieaves of Maxillaria infestans.
Gloeosporium epidendri' Henn. This organism attacks stems of Epidendrum sp.
Gloeosporium stanhopeŠ Allesch. is found on leaves of Stanhope e.
Gloeosporium laeliae Henn. is found on leaves of La lia sp.
Gloeosporium pallidum Karst. and Han occurs on leaves of Liparis longipes.
Colletotrichum orchidearum K. and H. appears on leaves of Bolbophyllum labbi, B. longiflorum. It is also found on foliage of Cymbidium sp., Physiophon loddigesii; Ezia stelleta, Coelogyne mayeriana, Pleurothallis tribuloides, Sarcanthus pugioniformis, on pseudobulbs of Eulophia saundersiana and on Oncidium pulvinatum.
Colletotrichum dicheae Henn. grows on foliage of Dichaea vaginata.
Colletotrichum roseolum Henn. develops on the pseudobulbs of Stanhopea oculata.
LEAF SPOT OF ORCHIDS
Caused by Cercospora angreci Roum.
Symptoms. This disease is usually manifested as spots which are more prominent on the underside of the leaves. As the affected foliage turns pale and loses its green color, the spots become covered with a chocolate-colored mold. The latter growth consists of the fruiting stalks and conidia of the fungus. Cercospora angreci is found on foliage of Odontoglossum alexandrae. Little is now known of the causal organism and of methods of control.
BLETIA LEAF SPOT
Caused by Volutella concentrica Hals.
Associated with the anthracnose (Colletotrichum bletiae) is often found a leaf spot which may be mistaken for it. The characteristic of this disease is the formation of large dark spots (fig. 59, a.). Each spot is made up of numerous bluish-colored concentric rings. The fruitings of the fungus appear as lemon-colored balls. It is not definitely known whether the Volutella fungus is an active or a weak parasite merely following some injury, or the attacks of a bacterial organism. In fact little study was given to this trouble and the only record that exists is a note by Halsted.
FUNGI FOUND ON ORCHID LEAVES
The following are fungi found by Hennings* on dead orchid leaves:
Physalospora orchidearum Henn. This fungus is found on dead stems of orchids of TainiŠ stellate and Lelia schilleriana. It is probable that the fungus Physalospora herbarum (Pers.) Rab, found on dead stems of Phajuswallichii is the same as P. orchidearum.
Pleospora orchidearum Henn. This fungus is found on dried-up stems of Phajuswallichii.
Nectria (Dialonectria) bolbophyli Henn. This fungus is found on dead pseudo-bulbs of orchids of Bolbophyllum lobbii.
Nectria behnickiana Henn. This was found on orchids imported from Brazil.
Macrophama oncidii Henn. This fungus was found on dead leaves of Oncidium pulvinatum.
Macrophoma cattleyicola Henn. This fungus was found on pseudo-bulbs of Cattleya labiata.
Diplodia sobrali r (Henn.) Taub. Found on dead leaves of Sobralia sessilis.
OTHER FUNGI FOUND ON ORCHIDS
Stibella bulbicola Henn. is found on pseudo-bulbs of Gomeza plantifolia, Stanhopea spec., Sarcanthus pugioniformis, Epidendrum spec. and on Oncidium pulvinatum.
Graphium bulbicola Henn. occurs on pseudo-bulbs of Oncidium pulvinatum.
Tubercularia cattleyicola Henn. grows on stems of Cattleya guttata.
Sclerotium orchidearum Henn. develops on stems of Vanda tricolor, and Dicha vaginata.
Diplodia bulbicola Henn. Found on dead pseudo-bulbs of Gomeza planifolia.
Zythia nepenthis Henn. Found on dead leaves of Nepenthes bicolorarta. Of the other fungi which are often found on dead foliage of Nepenthes may be mentioned Phyllosticta nepentheacearum Tassi, and Phoma nepenthis Cook and Mass. Humaria thozetti Berk., Excipularia epidendri Henn Found on dead foliage of Epidendron.
OXALIS (Oxalis bowiei)
Cultural Considerations. Oxalis is forced mainly as a window plant grown in baskets or pots. It requires a rich . soil and an abundance of water. The flowers open only when exposed to full light.
FUNGI RECORDED ON OXALIS
The Oxalis is a very hardy plant. The following are the fungi recorded on the host: Ăcidium oxalidis Thuem., Darluca filum (Biv.) Cast., Puccinia oxalidis Diet. and Ell., Urocystis oxalidis Pazs.
PALM (Phoenix spp.)
Cultural Considerations. Palms are very sensitive to wet and poorly drained pots or benches.
The soil best suited to palm culture is that which is made up of two-thirds rotted sod and one-third well rotted cow manure. Palms do poorly when treated with commercial fertilizers, and when its root system is disturbed, hence they should be repotted only when absolutely necessary. \Palms love partial shading (fig. 6o) and a moist atmosphere. The temperature should be allowed to go below 6o degrees F. at night. The foliage should be kept free from dust.
DISEASES OF PALMS
Forced palms are subject to less disease than those grown out of doors. Nevertheless, some of these indoor diseases often become very troublesome and serious.
Caused by Graphiola phoenicis Port.
Symptoms. Smut is a common disease on both greenhouse and outdoor palms of all sorts. The affected areas on the leaf become mottled with yellow, and upon the surface pustules appear (fig. 61, a.). These are cup-shaped conceptacles produced by the causal fungus, and in which the spores are borne. The spore pustules consist of a firm, dark colored exterior wall, enclosing a more delicate inner covering which contains a mass of thread-like filaments on which the spores are produced (fig. 61, b.). The spore pustules become very numerous and the affected foliage slowly shrivels.
Control. All diseased material should be destroyed by fire. Some florists recommend spraying or sponging the leaves with potassium permanganate.
Caused by Colletotrichum kentiŠ Hals.
This disease has been first studied by Halsted as it was found by him to attack the various ornamental Kentias.
Symptoms. The disease appears as watery spots, which soon become dry (fig. 61, h) and within which are formed the salmon-colored acervuli which contain numerous setŠ. In time the dead tissue falls out, leaving holes in which remain the hard, woody vessels which run across. This disease also attacks young seedlings and cripples them beyond any commercial value. The following Kentias are subject to the attacks of the anthracnose: Kentia belmoreana, K. canterburyana, and K. fosteriana.
Control. It is difficult to keep this disease in check unless the infected material is removed and destroyed by fire. Spraying the plants weekly with a standard fungicide will keep the anthracnose in check.
EXOSPORIUM LEAF SPOT,
Caused by Exosporium palmivorum Sacc. Symptoms. The disease is characterized by minute brown spots. These are often so numerous as to involve the entire leaf, causing it to dry up and die (fig. 61, c.). This trouble is very common on greenhouse palms, especially on those which are kept in too long under shade. It is common on Phoenix canariensis, on P. tenius and on P. reclinata. The disease undoubtedly must have been introduced from Europe with imported stock. Trelease observed it in America in 1897.
The Organism. The sporodochia are superficial black, and dense (fig. 61, d), visible to the naked eye as a black mold. The spores are borne singly, are olive brown in color, and are many times septate(fig. 61, e and f.).
Control. The disease seldom occurs in well lighted and well ventilated greenhouses. Where the disease makes its appearance, more attention should be given to the ventilation, and the shading should be gradually diminished. All infected material should be cut off and destroyed by fire; the plants should be sprayed with a standard fungicide.
Caused by Pestalozzia palmarum Cke.
Symptoms. This disease appears as transparent, dirty white spots at the tip of the leaflets or at the axils. The spots spread quickly and it is not uncommon to find numerous leaves killed, and the affected plant thereby badly disfigured. As the affected tissue dries, the spore masses are formed on the upper part of the leaflets and appear as a black exudate.
Control. Infected material should be cut out and destroyed by fire. Infected plants should not be syringed, for in this way the spores of the causal organism are spread wholesale. Spraying with a standard fungicide is also recommended.
Caused by Spharodithis neo washingtoniŠ.
The disease is mentioned by Smith as occurring in California. The leaves become covered with small elongated, black, slightly elevated spots (fig. 61, g.). Affected leaves should be removed and burned, and the plants sprayed with a standard fungicide.
PANSY (Viola tricolor).
Cultural Considerations. Pansies are grown mostly out of doors. Occasionally, however, florists raise them indoors as pot plants for purposes of window decoration. Its cultural requirements are about the same as for the violet (see p. 351).
DISEASES OF THE PANSY
Pansies, like violets, are subject to about the same diseases.
Caused by Colletotricham viola-tricoloris R. E. Sm.
Symptoms. The disease attacks the petals, and affected flowers become deformed, and fail to pro-duce seed. This is a serious consideration especially from the seedman's point of view. The spots on the leaves (fig. 62, a) are small with prominent margins.
The Organism. The acervuli are numerous, the stroma poorly developed, and the setae mostly single or in pairs, short, two septate and deep brown in color. The conidiophores are short, the conidia oblong or slightly curved, with blunt ends (fig. 62, b-f.).
Control. The disease is usually introduced with the seed. All shriveled seed should therefore be discarded, and the healthy ones soaked for five minutes in a solution made of one ounce of formaldehyde in twenty gallons of water. Diseased plants should be destroyed by fire. Pansy beds where anthracnose is present should be kept on the dry side of the house. The plants should not be sprinkled with water, as in this way the spores of the causal fungus may be spread about. Healthy plants may be protected by spraying with a standard fungicide.
Caused by Cercospora viola Sacc.
Symptoms. This disease appears as small dead spots surrounded by a definite black border. The spots soon enlarge and when very numerous cause the premature death of the foliage. The trouble is also met with on the blossoms; the petals in this case become spotted and blotched. Affected young blossoms become distorted or fail to open altogether.
The Organism. The conidiophores of the fungus are short, simple and grayish. The conidia are long, slender, rod shaped, hyaline, and many septate.
Control. It is claimed by Stone and Smith that good results were obtained by spraying with Bordeaux. The latter, however, is objectionable be-cause of its staining the blossoms. Ammoniacal copper carbonate may therefore be used instead. Spraying may be done at intervals of every two weeks. All dead and infected material should be destroyed by fire.
Caused by Fusarium violae Wolf.
This disease causes a rot of the roots and stems. The causal organism (fig. 62, g to i) is usually brought in the house with infected compost. As a control measure soil sterilization is recommended (see pp. 32-43).
Caused by Rhizoctonia solani Kuhn.
Crown rot first appears in the form of minute lesions at the crown of the plant. These enlarge and penetrate the tissue deeply until the plant is practically girdled. Rotting usually sets in, where-upon the prostrate branches, the leaves, and petioles also rot. For a description of the causal organism and for methods of control, see p. 20.
PANDANUS OR SCREW PINE (Pandanus veitchii)
Cutural Considerations. Screw pines are forced extensively and are used as ornamental house plants. They require a temperature of 65 to 70 degrees F. and must be exposed to full light, especially in the winter. The plant flourishes best in a soil composed of two parts of heavy loam and one part of thoroughly rotted cow manure. The soil required is a heavy loam to which is well worked in one-third of thoroughly rotted cow manure.
Diseases of the Pandanus. Pandanus is considered a very healthy plant. There are, however, two fungi that proved injurious; these are Nectria pandani Tul. and Melanconium pandani Lev., which are known to be parasites.
POINSETTIA (Euphorbia pulcherima)
Cultural Considerations. Poinsettias are extensively grown for the Christmas trade. The plants prefer a soil consisting of fibrous loam, one-fourth of which is well rotted cow manure. Poinsettias require frequent repotting to prevent them from be-coming potbound. The night temperature should never go down below 55' degrees F. As the plants advance in age, the temperature is raised to 65 or 70 degrees. A few days before Christmas the stock should be ready and the temperature lowered to 50 degrees F. Great care should be exercised to prevent the potted plants from becoming either overwatered or too dry. Poinsettias that are to be used for cut flowers should have the stem end dipped in hot water for a few moments and then placed in cold water. This procedure will cauterize the wounds and thus will add to the keeping qualities of the blossoms.
DISEASES OF POINSETTIAS
Poinsettias seem to be remarkably free from dis-eases. This is especially true as the plants outgrow the cutting stage.
Caused by Rhizoctonia solani Kuhn.
Symptoms. The trouble is confined mostly to cuttings that have been planted in an infected soil. The lesions unite and in nearly every case form a collar around the stem on the surface of the soil. The collar formed is narrow, depressed, and dark in color. For a description of the causal organism and methods of control, see p. 20.